The present invention relates to an image forming apparatus such as a printer and a copier using an electro-photography method for forming an image on a recording medium.
In a conventional image forming apparatus, using toner in a plurality of colors, for example, four colors, toner images are formed on a photosensitive member corresponding to toner in a plurality of colors. Then, the toner images are sequentially transferred to a sheet or a recording medium.
In the conventional image forming apparatus, a belt transports the sheet to the photosensitive member, so that the toner images formed on the photosensitive member are transferred to the sheet. In this case, when the belt moves at a speed different from that of the photosensitive member, the toner images may be shifted with each other, i.e., color shift. To this end, there has been proposed another conventional image forming apparatus, in which a photosensitive member and a belt are controlled to move at a same speed.
In the conventional image forming apparatus, in which the photosensitive member and the belt are controlled to move at a same constant speed, until the photosensitive member is accelerated and reaches the constant speed, the photosensitive member needs to move for a distance longer than that of the belt until the belt reaches the same constant speed. Accordingly, the belt tends to receive excessive tension. As a result, when toner images are transferred to a sheet, the toner images tend to be shifted, thereby causing color shift.
In view of the problem described above, an object of the invention is to provide an image forming apparatus, in which it is possible to prevent a belt from receiving excessive tension when a photosensitive member is accelerated. Accordingly, it is possible to prevent toner images from being shifted when the toner images are transferred to a sheet, thereby preventing color shift.
Further objects and advantages of the invention will be apparent from the following description of the invention.